This disclosure relates generally to the field of drilling wells through subsurface formations. More specifically, the disclosure relates to apparatus for controlling release of fluids from such wellbores, such devices called blowout preventers (BOPs).
BOPs known in the art have one or more sets of opposed “rams” that are urged inwardly into a housing coupled to a wellhead in order to hydraulically close a wellbore under certain conditions or during certain wellbore construction operations. The housing may be sealingly coupled to a wellhead or casing flange at the top of the well. The rams, when urged inwardly, may either seal against a pipe string passing through the BOP and/or seal against each other when there is no pipe (or when the pipe is present but must be cut or “sheared.” Movement of the rams is performed by hydraulically operated actuators.
BOPs known in the art used in marine operations may be coupled to a wellhead at the bottom of a body of water such as a lake or the ocean. In such BOPs, electrical power may be supplied from a drilling unit above the water surface, which may be converted to hydraulic power by a motor operated pump proximate the BOP. There may also be hydraulic oil tanks having hydraulic fluid under pressure proximate the BOP in order to provide the necessary hydraulic pressure to close the rams in the event of failure of the hydraulic pump or drive motor.
A typical hydraulically actuated BOP is described in U.S. Pat. No. 6,554,247 issued to Berkenhof et al.